This invention relates to a voltage regulator for a charging generator. More particularly, the present invention relates to a voltage regulator for a charging generator which is mounted to an automobile and suppresses a high voltage generated when disconnection of the output wires of the generator occurs.
A voltage regulator for a charging generator regulates the output voltage of the generator for charging a battery and holds the battery voltage connected to the generator at a predetermined level. The voltage regulator compares the battery voltage with a reference voltage and regulates the voltage. In this case, if disconnection of connecting wires connecting the generator to the battery occurs, the power is not fed to the battery and hence, the battery voltage drops. Accordingly, the output voltage of the generator rises so as to raise the battery voltage. When the voltage of the generator becomes a high voltage, the load connected directly to the output of the generator undergoes breakage or is burnt out. To solve this problem, the regulator is constructed so that when the output voltage of the generator exceeds a predetermined voltage, the operation of the generator is stopped. This construction is known in the art from Japanese Patent Laid-Open No. 157942/1980, for example. In the case where a heavy load is connected to the battery, the output voltage of the generator will rise if this heavy load is drastically released. Accordingly, the voltage which stops the generation of the generator must be set to a voltage higher than the voltage which rises when the load is released, since otherwise the operation of the generator will be stopped undesirably whenever the heavy load is released. However, if the voltage for stopping the generator operation is set to a high level, an undesirably high voltage will be impressed upon the load in a case where the connecting series between the generator and the battery become broken.